The inventive concept relates to photomasks used in fabrication of semiconductor devices, and more particularly, to reflective photomask blanks used in extreme ultraviolet (EUV) photolithography processes and reflective photomasks obtained from the reflective photomask blanks.
The wavelength of light used in a photolithography process (i.e., an exposure process) has been continuously reduced due to the decrease in design rules of semiconductor devices. Thus, an extreme ultraviolet (EUV) ray having a relatively short wavelength with respect to a beam having a wavelength of g-line or i-line has been used in the exposure process of a EUV lithography process. The EUV lithography process may be performed using a reflective exposure system including reflective EUV photomasks to transfer patterns of each reflective EUV photomask onto a wafer.
The EUV ray used in the EUV lithography process may be more readily absorbed into most material layers. Thus, it may be difficult for the reflective EUV photomasks to employ a pellicle which is widely used to protect the patterns of general photomask used in exposure processes that utilize an argon fluoride (ArF) laser or a krypton fluoride (KrF) laser as a light source. Accordingly, reflective EUV photomasks may be more readily contaminated by particles in the air and by carbon atoms which are a process byproduct due to a relatively high energy of the EUV ray. That is, the reflective EUV photomasks have to be periodically cleaned. As a result, improved photomasks may be still required to have increased life times and be free of physical damage and reflectivity degradation even though the exposure process and the cleaning process are repeatedly applied thereto.